Apply suggestions from code review

Co-Authored-By: Nick Robinson <npr251@gmail.com>

Author: oxinabox

docs/src/debug_mode.md

@@ -1,13 +1,13 @@
 # Debug Mode
 
-ChainRules supports a *debug mode* which you can use while writing new rules.
+ChainRulesCore supports a *debug mode* which you can use while writing new rules.
 It provides better error messages.
 If you are developing some new rules, and you get a weird error message,
 it is worth enabling debug mode.
 
 There is some overhead to having it enabled, so it is disabled by default.
 
-To enable redefine the []`ChainRulesCore.debug_mode`](@ref) function to return `true`.
+To enable, redefine the [`ChainRulesCore.debug_mode`](@ref) function to return `true`.
 ```julia
 ChainRulesCore.debug_mode() = true
 ```

src/debug_mode.jl

@@ -1,5 +1,5 @@
 """
-    debug_mode()
+    debug_mode() -> Bool
 
 Determines if ChainRulesCore is in `debug_mode`.
 Defaults to `false`, but if the user redefines it to return `true` then extra